Barnett, Rodger Phillip; (1993) Controlled release of oxaminiquine from polymer films. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

A Study has been made of the physicochemical properties of Eudragit Retard L (ERL) and Eudragit Retard S (ERS) copolymers that influence the release of the schistosomicidal agent, oxamniquine (Pfizer UK4271) when dispersed in the polymers. Isolated films were produced by casting solutions of the mixed polymers in dichloromethane on to a mercury surface and allowing the solvent to evaporate. The presence or absence of crystallinity within the polymer films was determined by X-ray crystallography and samples of the isolated films were examined by scanning electron microscopy to study their surface characteristics. The glass transition temperatures of polymer films were determined by measurement of the surface hardness over a range of temperatures using a micro-indentation hardness tester. A series of films containing dispersed oxamniquine were prepared and the diffusion of oxamniquine from the films into a buffered aqueous medium was measured. To extend the studies from these model systems to a suitable dosage form, the polymers containing dispersed oxamniquine were spray coated onto inert, spherical carbohydrate pellets in a laboratory scale fluidised bed coater/granulator. The factors affecting the release of oxamniquine from the free films and coated pellets were critically evaluated. The parameters which were studied included the proportion of polymer ERL to ERS, the drug loading within the film, and the effect of plasticising agents. The plasticisers chosen were glyceryl triacetate, polyethylene glycol 400, and dimethyl, diethyl and dibutyl phthalates. It was found that the release from coated pellets was faster than from the equivalent free films, and no direct correlation could be made between the model systems and formulated dosage forms. The data from the release profiles was optimised mathematically to arbitrary polynomials by computer. The fitted data were tested against various kinetic models to evaluate the possible mechanisms of release of oxamniquine from both the free films and coated pellets.

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